(1) Field of the Invention
The present invention relates to an amorphous, spherical inorganic compound comprising as main constituents (1) an oxide of at least one metal selected from the group consisting of metals of the Groups I, II, III and IV of the Periodic Table and (2) silica, and a process for the preparation thereof.
Incidentally, by the term "amorphous compound" is meant a compound having a crystallinity lower than 50%.
(2) Description of the Prior Art
Powdery inorganic compounds comprising as main constituents a specific metal oxide and silica have been known. It has also been known that these inorganic compounds can be prepared according to a method comprising mixing silica with a metal oxide, melting the mixture at a high temperature higher than the melting point of the mixture to obtain a vitreous substance and pulverizing the vitreous substance. The powdery product obtained according to this known method, however, has an indeterminate shape and a very broad particle size distribution, and therefore, it can be applied only to much limited uses. As another method, there is known a method comprising mixing a silicon alkoxide with a titanium alkoxide, hydrolyzing these alkoxides to obtain a gel and sintering the gel product to obtain an inorganic compound composed of silica and titania [see Nippon Kagaku Kaishi, 10, 1571 (1981)]. This method is advantageous over the above-mentioned method in that the gel can be formed into various shapes, for example, a plate and a fiber. Even if this method is adopted, however, it is impossible to obtain an amorphous inorganic compound having a spherical shape, a small particle size, for example, from 0.1 to 1.0 .mu.m and especially a narrow particle size distribution. In other words, it has been an important technical problem how to obtain an amorphous, spherical inorganic compound uniform in the particle size, which comprises as main constituents silica and a metal oxide.